The present invention relates to a cemented carbide body for use in, e.g., twist drills, particularly useful for metal cutting operations requiring high wear resistance such as drilling in cast iron, etc.
Drilling in metals is generally divided into two types: long hole drilling and short hole drilling. Short hole drilling is generally meant drilling to a depth of up to 3-5 times the drill diameter.
Long hole drilling places great demands on good chip formation, lubrication, cooling and chip transport. This is achieved through specially developed drill systems with specially designed drill heads attached to a drillstring. The drill head can be of solid cemented carbide but is generally of tool steel provided with a number of inserts of cemented carbide placed in such a way that they together form the cutting edge.
With short hole drilling, the demand is not as great and twist drills either of cemented carbide, tool steel or tool steel provided with cemented carbide inserts are used.
A twist drill of cemented carbide is usually manufactured from a cylindrical blank which is machined to the desired shape and dimensions particularly to form cutting edges and flutes. Alternatively, the chip flutes are at least preformed during the extrusion operation. As a result of the grinding, sharp edges are formed.
A relatively recent type of drill is a drill with an exchangeable drill tip generally made of cemented carbide and removably connected to a drill shank of tool steel.
A common reason to failure of a twist drill is excessive wear in the juncture between the main cutting edge and the leading edge. Another reason to failure is, when the cutting speed is increased, plastic deformation due to high temperature in the peripheral part of the cutting edge.
EP-A-951576 discloses a cemented carbide drill consisting of a tough core surrounded by a more wear resistant cover. This type of drill is most suitable for toughness demanding drilling applications.